An industrial production of laurolactam by Beckmann rearrangement reaction of cyclododecanone oxime generally employs concentrated sulfuric acid or oleum as a rearranging agent. However, it is necessary to use sulfuric acid in an equimolar amount to the oxime and to, after the reaction, neutralize sulfuric acid with a base such as ammonia, which causes that a large amount of ammonium sulfate is formed as a byproduct. The process, therefore, requires facilities for producing concentrated sulfuric acid and oleum and for treating ammonium sulfate, which is a process with significant environmental burden and facility cost (Patent Document No. 1, Patent Document No. 2).
For solving such a problem, various catalyst reaction systems have been investigated. For example, there have been described Beckmann rearrangement reaction using cyanuric chloride as a catalyst (see Patent Document 3 and Non-patent Document 1), rearrangement of the oxime in the presence of a dialkylamide compound and phosphorous pentoxide (see Patent Document 4), rearrangement of the oxime in the presence of a dialkylamide compound, phosphorous pentoxide and a fluorine-containing strong acid (see Patent Document 5), rearrangement of the oxime in the presence of a dialkylamide compound, a condensed phosphoric acid compound and optionally a fluorine-containing strong acid (see Patent Document 6), rearrangement of the oxime in the presence of a dialkylamide compound, phosphorous pentoxide or a condensed phosphoric acid compound, and a non-fluorinated sulfonic anhydride (see Patent Document 7), rearrangement of the oxime in the presence of a dialkylamide compound, an inorganic acid and a carboxylic anhydride (see Patent Document 8), and rearrangement of the oxime in the presence of an acid anhydride under the condition that the total molar amount of water contained in a reaction system is 15 or less to that of the acid anhydride (see Patent Document 9). However, most of the processes employ a particular catalyst or solvent for which a recovering or recycling method has not been explicitly described and are thus imperfect as an industrial process.
Those that are relatively inexpensive and readily available as industrial chemicals include cyanuric chloride, phosphorous trichloride, phosphorous pentachloride and thionyl chloride. Among these, cyanuric chloride, phosphorous trichloride and phosphorous pentachloride are converted, when inactivated, into compounds insoluble in an organic solvent such as cyanuric acid and phosphoric acid, and therefore when being used in a large amount, they cause pipe blockage or poor heat transfer in an industrial process, and thus they are undesirable. In contrast, since thionyl chloride is finally decomposed to generate hydrogen chloride and sulfur dioxide without solid precipitation, a simple industrial process can be formed.
In terms of Beckmann rearrangement of an oxime compound using thionyl chloride as a catalyst, Patent Document Nos. 11 and 12 have disclosed a process wherein a mixture of thionyl chloride and an oxime compound is heated. It has been, however, found that in the process, a yield varies depending on, for example, a temperature-increase rate and a yield itself is low. In addition, Beckmann rearrangement is a severely exothermic reaction, which cannot be controlled by the process described in Patent Document Nos. 11 and 12 and cannot be expanded to an industrial scale. Furthermore, a process in which thionyl chloride is added to a solution of an oxime compound heated to a predetermined temperature does not provide a target amide compound in a good yield. Therefore, further improvement is required.